Danish inventor Peter Madsen has fronted court charged with manslaughter after his giant homemade submarine sunk with a passenger inexplicably missing. The submarine only sunk after it was found by searching authorities.

A Danish court has ordered the owner of an amateur-built submarine be held in pre-trial detention for 24 days while authorities investigate the mystery disappearance of a Swedish journalist who was aboard the vessel before it sank.

Peter Madsen faces manslaughter charges over the disappearance of the female journalist.

Thirty-year-old freelance journalist Kim Wall was doing a story on the submarine. The inventor told authorities Friday that he dropped Wall off on an island in Copenhagen's harbor before the vessel sank.

The submarine was located Friday at a depth of seven meters (22 feet) south of Copenhagen. Divers were initially unable to safely enter it.

A salvage vessel was working Saturday to raise the submarine.

Crowdfunding project

Madsen built the world's largest homemade submarine in 2008 after crowdfunding the cost. The 40-ton, 18-meter-long craft named UC3 Nautilus was his third submarine project.

According to a timeline compiled by police, on Thursday at about 7 p.m. local time (1700 UTC), the sub departed Refshale Island, a former industrial shipyard transformed into a creative hub, for what was supposed to be a short trip.

When it failed to return, the journalist's boyfriend alerted authorities at about 2:30 a.m. Friday morning, prompting a wide search.

Craft sinks after being spotted

Two helicopters and three ships scoured the Baltic Sea waters between Copenhagen and the island of Bornholm. Eventually a lighthouse in Koge Bay, about 30 kilometers (19 miles) south of Copenhagen, spotted the craft at 10:30 a.m. on Friday.

"A radio contact was established for the boat, which, according to the owner, was heading towards the harbor," the police statement said. But 30 minutes later "the submarine suddenly sank and the owner was subsequently rescued on a private motorboat sailing him in port."

Local broadcaster TV2 aired footage of Madsen getting off the private boat and giving a thumbs-up sign, but the journalist was nowhere to be seen.

Madsen told authorities he had dropped her off back at their departure point at about 10:30 p.m.

"Whether the woman was on board the submarine at the time of her disappearance is unclear," Danish police said without naming her.

Ignored radio contact

When asked why he did not respond to radio contact earlier in the day, Madsen told them he had had technical problems, Danish navy spokesman Anders Damgaard told The Associated Press news agency.

Before his arrest, Madsen told TV2 that the submarine sank when a minor ballast problem rapidly escalated and sunk the boat.

"It took about 30 seconds for Nautilus to sink, and I couldn't close any hatches or anything," he said. "But I guess that was pretty good, because I otherwise still would have been down there."

"I am fine, but sad because Nautilus went down."

Copenhagen Deputy Police Inspector Jens Moller Jensen said investigators were looking for witnesses who may have seen the woman after the time Madsen reported she disembarked.